"Linux Gazette...making Linux just a little more fun!"

A Visual Packet Monitor

Introduction

For the past few years I've used internal modems, but I still miss the
flickering lights on the first modem I ever used, an external unit which
seemed fast at the time. One of these lights indicated incoming data-packets
while another showed the outgoing. The advantages of these inobtrusive
lights were that they didn't occupy screen real-estate and they could be monitored
with peripheral vision.

Recently Matthew Bevan released a new version of NetLED, a small utility
which monitors any of several interfaces such as PPP, SLIP, or ethernet using
the keyboard's light emitting diodes (LEDs). This is a great idea, since
these LEDs aren't particularly useful in their native state. I've never had
any use for the Caps Lock key, or its LED; I like to have that key generate
the Escape key key-code (easing VI mode-switching), which leaves its LED open
for alternate uses such as NetLED.

NetLED is a tiny program (meant to be run as a daemon) which can be left
running even when a network interface is inactive. The command syntax is
simple:

netled [console] [interface]

As an example, I use it to monitor activity on a dial-in PPP
connection:

netled console ppp0

The console parameter, if just "console" is specified,
allows the LEDs to flash on all consoles, while ppp0 tells the program
to monitor the first PPP device. Substitute eth0 in order to monitor
the first ethernet device.

A strongly worded warning in the README file encourages the user to follow
the recommended syntax:

NOTE: DO NOT PREPEND /DEV/ TO ANY OF THE DEVICES!!!
I MOCK ANYONE WHO ASKS ME HOW TO FIX THEIR COMPUTER
WHEN THEY ARE DOING THIS!
PROPER: netled console lo
NOT: netled /dev/console /dev/loop0

I'm curious as to the nature of the dire consequences implied by this
warning, but not curious enough to try it!

NetLED can be started manually (I've aliased 'netled console ppp0'
to 'led') or it could be started in either an init script or as an
addition to a PPP start-up script.

If you would like to try it out, the source code can be obtained from this
WWW site: